Hydraulic circuit leak detector and shut-off mechanism

ABSTRACT

A leak detector and shut-off apparatus shuts off hydraulic fluid downstreamo prevent the hazards attendant hydraulic failure such as loss of fluid and fire. A first sensor is coupled to a supply line for hydraulic fluid to produce pressure differential force F s , which is representative of the flow of hydraulic fluid. A second sensor is coupled to a return line for hydraulic fluid to produce pressure differential force F r  that is representative of flow of hydraulic fluid. A compensator creates representation F c  of the rate of accumulation of hydraulic fluid in the hydraulic circuit downstream of the device and a safety margin. A shutoff mechanism is connected to the first and second sensors and the compensator to shut off the supply and return lines when F s  is greater than the sum of F r  and F c . Mechanical and electrical designs shutoff or isolate downstream hydraulic actuators, branches or select components immediately when a leak is detected to prevent loss of fluid and to reduce the hazards of fire.

STATEMENT OF GOVERNMENT INTEREST

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION

Hydraulic systems are many and varied in design. Typically, they havebeen used to control remote mechanisms and control surfaces. Mostaircraft rely on hydraulic systems to transmit forces and motion frompilot commands to control surface movements. The aircraft utilizeseveral mechanisms to protect hydraulic systems in case of pressureloss. Most of these safeguards are responsive to loss of pressure in theclosed system (i.e., loss of pumps). However, aircraft that are damagedand develop hydraulic leaks elsewhere in a hydraulic ensemble may loseone or all of the constituent hydraulic systems. The design of manycontemporary hydraulic systems is such that a leak in a branch of asystem may result in the complete loss of that system. This type loss,while leaving basic flight control to the backup systems, may result inreduced handling qualities and make mission completion and safe flightimpossible. Additionally, any leak in a hydraulic system has thepotential for causing fires that can have catastrophic results.

Reservoir level sensing has been and is relied upon to disconnectleaking hydraulic systems. Sensors located in the hydraulic reservoirsdetect leaks by sensing the level of hydraulic fluid in the reservoirs.If the level in any reservoir is decreasing, the hydraulic systems areshut down one by one exclusively until the level stops decreasing.Obviously, this method takes time and shuts down entire systems. Therelatively long time to isolate the problem can lead to hydraulic fire,and this technique will shut down an entire system, not only the linesthat are affected.

Check valves are inserted in some hydraulic systems to guard against thehazards associated with hydraulic fluid leakage. Check valves limit flowin one direction. If upstream hydraulic pressure is lost, the itemsdownstream of the check valve can still be pressurized from anothersource. The problem with this approach is that if pressure is lostdownstream from the check valve, it will not close and all of the fluidmay be lost or a fire might result. Isolation valves are added in somesystems to afford a limited degree of protection. These valves allowcomponents of the hydraulic system that are not being used to be shutoff from the rest of the system. In aircraft, for example, isolationvalves limit the load a particular system has during flight. Typically,they are restricted to the landing gear and wing fold systems. Isolationvalves provide limited leakage protection. They are usually designedwith a backup pump within the isolated branches that gives emergencypower to the isolated system when the primary hydraulic supply systemloses pressure. The major limitation of using isolation valves in thismanner is that if the isolated system sustains damage and leaks, theleak will not be detected until the isolation valve is opened and thesupply system begins to lose fluid. For example, the isolation valve forthe landing gear and wing fold systems is not opened until the approachfor landing. At this time the workload is high and precision flight isessential. Failure of a hydraulic system at this time is catastrophic.

Switching valves are relied upon to switch system pressurization to analternate system when the primary system loses pressure. The problemwith using switching valves becomes apparent from the following: if ahydraulic actuator leaks in a primary system and this defective actuatorwere switched to be pressurized by a backup or alternate system, thissystem would also leak.

Hydraulic fuse systems are used successfully only in limited areas. Ahydraulic fuse functions very similarly to an electrical fuse. When anexcessive flow is measured over a period of time, then the device shutsdown the line. The major limitation of a hydraulic fuse is that it hasrelatively long response and reset times. These durations cannot betolerated when dealing with the highly dynamic flows in the flightcontrols for aircraft. Usually, this device is restricted to "static"systems on the aircraft such as the wheel brakes, landing gear extensionsystems, and lines to pressure gauges.

Therefore, in accordance with this invention a need in the state of theart has been discovered for an apparatus that will nearlyinstantaneously detect leaks and in a branch, circuit, or component of ahydraulic system and immediately shut off the flow of hydraulic fluid tothe affected branch, circuit, or component and leave hydraulic pressurefor the rest of the elements in that system.

SUMMARY OF THE INVENTION

The present invention is directed to providing an apparatus for shuttingoff a hydraulic circuit. A first sensor coupled to a supply line forhydraulic fluid produces a force F_(s) that is representative of theflow of hydraulic fluid. A second sensor coupled to a return line forhydraulic fluid produces a force F_(r) that is representative of theflow of hydraulic fluid. A compensator creates a force F_(c) that isrepresentative of the rate of accumulation of hydraulic fluid in thehydraulic circuit. A shut-off mechanism is connected to the first andsecond sensors and the compensator to shut off the supply line andreturn line when F_(s) is greater than F_(r) +F_(c).

A prime objective of the invention is to provide a safety feature forhydraulic systems.

Another objective of the invention is to provide a safety feature forhydraulic systems that reduces hydraulic fluid leakage.

Another objective is to provide a mechanism that reduces the hazardsassociated with leaking fluid.

Still another objective of the invention is to provide a safety featurefor hydraulic systems that reduces the possibility of fire.

Another objective is to provide a mechanism for a hydraulic system thatimmediately shuts down supply and return lines in a hydraulic circuitwhen leakage occurs.

Yet another objective is to provide an apparatus that immediatelydisconnects hydraulic equipments when leakage occurs to reduce the lossof hydraulic fluid and possibility of fire.

Another objective of the invention is to provide leakage detection andisolation within a hydraulic system to allow continued operation of thatsystem.

These and other objectives of the invention will become more readilyapparent from the ensuing specification and drawings when taken with theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 sets forth a schematic cross-sectional representation of oneembodiment of the hydraulic fluid leak detector and shut-off apparatusof this invention.

FIG. 2 shows the apparatus of FIG. 1 in the shut-off position.

FIG. 3 depicts an alternate design for a shut-and-lock mechanism.

FIG. 4 depicts another embodiment of the invention employing someelectrical components in the hydraulic fluid leak detector and shut-offapparatus of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 of the drawings, hydraulic fluid leak detector andshut-off apparatus 10 of this invention is based on the principle ofconservation of mass. Apparatus 10 measures the mass flow of hydraulicfluid going to and coming back from an actuator, hydraulic circuit orother hydraulic component in a hydraulic circuit, not shown in thedrawings. The apparatus is designed to shut off or isolate an actuatorin the event of hydraulic leakage. It does that by sensing mass flowdifference that is greater than the designed imbalance of the hydraulicactuators or other mechanisms. When this difference is sensed, theapparatus immediately shuts down and cuts off flow of hydraulic fluid tothe leaking circuit.

Hydraulic fluid leak detector and shut-off apparatus 10 is depicted incross section. Apparatus 10 is shown in the open position that allowshydraulic fluid to flow uninterrupted to non-leaking hydrauliccomponents located downstream. The term downstream refers to thatportion of the hydraulic circuit that is to the right of apparatus 10 Ahydraulic fluid supply line 20 and a hydraulic fluid return line 30transmit flowing hydraulic fluid as indicated by flow arrows 21 and 31.Supply line 20 and return line 30 respectively extend through apparatus10 in line portions 20a and 30a and downstream line portions 20b and30b. These line portions connect hydraulic fluid as indicated by flowarrows 22 and 32 to and from a downstream actuator (not shown).Apparatus 10 is designed to shut off or close portions 20a and 30a fromany hydraulic components that are downstream from the apparatus andconnected to portions 20b and 30b

A pair of Bernouilli devices 40 and 50 are connected in supply line 20and return line 30, respectively. The Bernouilli devices are identical,but could be different if desired in different design applications.Bernouilli devices 40 and 50 have ports connected to hydraulic conduits41 and 42 and 51 and 52 extending to corresponding ports in linearpiston cylinder 60.

Cylinder 60 consists of a cylinder casing 61 divided into fivecylindrically-shaped compartments 62, 63, 64, 65, and 66. Thecompartments are separated by walls 67, 68, 69, and 70, that each have abore 67a, 68a, 69a, and 70a, respectively. The bores are aligned witheach another and are sized to slidably accommodate an elongate shaft 75in a sealed relationship. An appropriate sealing structure, such asO-rings, sealing rings, sealing packing, sealing compounds, etc. can beincluded between bores 67a, 68a, 69a, and 70a and shaft 75, as will beapparent to one skilled in the art. Shaft 75 is positioned to extendthrough all of the bores. Shaft 75 is affixed to valve-pistons 76 and 77in compartments 62 and 63, to pressure pistons 78 and 79 in compartments64 and 65, and to shut-and-lock mechanism piston 80 in compartment 66.The circumferential outer surface of each piston slidably adapts to thecylindrical inner surface of the five compartments in a sealedrelationship. An appropriate sealing structure, such as O-rings, sealingrings, sealing packing, sealing compounds, etc. can be included betweenpistons 76, 77, 78, 79, and 80 and the inner walls of compartments 62,63, 64, 65, as will be apparent to one skilled in the art.

Shaft 75 is biased toward an open position by pre-compressed spring 85in compartment 65 which also contains piston 79. The pre-compressedspring functions as a compensator that exerts a compensating force F_(c)between piston 79 and wall 69. This force is transmitted to valve-piston77 causing it to rest against wall 68 keeping portions 20a and 30a open.Compensation force F_(c) is representative of the rate of accumulationof mass of hydraulic fluid (plus a safety margin) in an actuatordownstream from linear piston cylinder 60. Consequently, when theactuator downstream becomes unbalanced, pre-compressed spring 85 willresist circuit shutoff up to a designed mass flow imbalance of theactuator plus a safety margin.

Piston 80 is interconnected to shaft 75 and functions as a shut-and-lockmechanism. Conduits 66a and 66b connect compartment 66 to supply line 20and return line 30, respectively. A leak downstream of arrangement 60will cause shaft 75 to move in the downstream direction, in this case tothe right of the drawing. This will displace piston 80 and open conduit66a to the supply line pressure. This will cause a pressure differenceacross piston 80 that will force valve-pistons 76 and 77 to move to theright and close return line 30 and supply line 20 at portions 20a and30a, respectively, see FIG. 2. Since compartments 62 and 63 are filledwith hydraulic fluid, valve-pistons 76 and 77 are respectively providedwith ducts 76a and 77a to allow the valve-pistons to be displaced intheir compartments. Valve-pistons 76 and 77 will remain closed untilsupply pressure within line 20 is shut off.

Referring again to FIGS. 1 and 2, in operation, linear piston cylinder60 effectively shuts off hydraulic fluid to and from a downstreamactuator or other hydraulic device. Supply line 20 transmits hydraulicfluid, as represented by the arrow 21 from a remote pump, not shown,through Bernouilli device 40, into compartment 65, through portion 20a,and through portion 20b of supply line as represented by the flow arrow22. As the hydraulic fluid passes through Bernouilli device 40, the flowof hydraulic fluid creates a pressure differential P_(S) betweenconduits 41 and 42 based on Bernouilli's Principle. Pressuredifferential P_(s) is transmitted via conduits 41 and 42 to cylindercompartment 65 which contains piston 79. P_(s) is converted to forceF_(s) on piston 79 by the relationship that force equals pressure timesarea. This force is transmitted to the piston in the direction shown inFIGS. 1 and 2.

Simultaneously, return line 30 is transmitting returning hydraulic fluidcoming from the actuator. Return line 30b transmits hydraulic fluid, asrepresented by the arrow 32 from the actuator, not shown, throughportion 30a, through Bernouilli device 50, into compartment 64, andthrough return line 30 as represented by the flow arrow 31. As thehydraulic fluid passes through Bernouilli device 50, the flow ofhydraulic fluid creates a pressure differential P_(r) between conduits51 and 52 based on Bernouilli's Principle. Pressure differential P_(r)is transmitted via conduits 51 and 52 to cylinder compartment 64 thatcontains piston 78. P_(r) is converted to a force F_(r) on piston 78 bythe relationship that force equals pressure times area. As shown in thedrawings, force F_(r) is opposite in direction to force F_(s) that isexerted against piston 79.

Differential pressures P_(s) and P_(r) and consequent forces F_(s) andF_(r) exerted against pistons 79 and 78 are generated according toBernouilli's Principle and the conservation of mass. These forces aredirect functions of the rate of flow of hydraulic fluid or mass flowthrough the supply and return lines, respectively. If the Bernouillidevices are identical and no mass accumulates in the actuator, themagnitudes of P_(r) (F_(r)) and P_(s) (F_(s)) will be equal. If,however, there is some accumulation of mass of hydraulic fluid in theactuator, P_(s) will not equal P_(r) and the differential forces willvary depending on the stroke of the actuator. If the stroke of theactuator causes the mass flow of hydraulic fluid through supply line 20to be greater than the mass flow of hydraulic fluid of return line 30,then P_(s) (F_(s)) will be greater than P_(r) (F_(r)). However,pre-compressed spring 85 will exert its compensating force F_(c) andprevent shaft 75 from moving as long as the mass flow of hydraulic fluidis within the design limits of the actuator. If the actuator is on astroke that gives up its accumulated mass of hydraulic fluid, P_(r) willbe greater than P_(s). However, this will not result in any movement inthe shaft 75 because piston 77 is resting against wall 68 that separatescompartments 63 and 64.

If a leak occurs in portion 20b of the supply line downstream ofapparatus 10b, considerably more hydraulic fluid flows throughBernouilli device 40 than through Bernouilli device 50. Based onBernouilli's Principle, therefore, P_(s) and thus force F_(s) will begreater than force F_(r) created by P_(r). Consequently, pre-compressedspring 85 and pistons 76, 77, 78, 79, and 80 affixed to shaft 75 willbegin to move in the right. As piston 80 moves to the right, supply linepressure is fed to one side of the piston via interconnect 66a anddisplaces piston 80 until it rests against stops 66a' in compartment 66,see FIG. 2. This motion of piston 80 to the right displaces shaft 75 andvalve-pistons 76 and 77 to shut portions 20a and 30a of the supply andreturn lines. This action shuts off all hydraulic fluid flow downstreamof apparatus 10.

If there is a leak in portion 30b of the return line downstream ofapparatus 10, fluid flows through Bernouilli device 40. However, verylittle, if any, fluid will flow through Bernouilli device 50. Thiscauses the same displacement of shaft 75 and its connected structuresand results in shutoff in portions 20a and 30a of the supply and returnlines as described in the previous paragraph with respect to a supplyline leak.

Note that apparatus 10 is designed to detect leaks downstream of itslocation. Any leaks upstream will not be detected. Apparatus 10 isdesigned to be located at the beginning of branches in a hydraulicsystem, or before any other particular element of component in ahydraulic system that should be isolated when it leaks.

FIG. 3 shows an alternate design for piston 80. Piston 90 is shown in analternate design of a shut-and-lock mechanism and it is provided with acircumferential groove 91. A pre-compressed spring 92 is held between aninner surface of casing 61 and an inner cylinder 93. The inner cylinderis held in place by ball bearings 94 wedged into a pair of cuts 95provided in casing 61. As piston 80 moves in the downstream directiondue to failure of the hydraulic actuator, for example, ball bearings 94are forced into openings 96 provided in inner cylinder 93 and intogroove 91. This frees inner cylinder 93 from casing 61 and attaches itto piston 90. The force exerted by pre-compressed spring 92 againstinner cylinder 93 drives piston 90 and shaft 75 to the far right whichshuts off portions 20a and 30a by valve-pistons 77 and 76, respectively.All hydraulic fluid flow downstream of apparatus 10 is shut off. Notethat this design will keep valve-pistons 76 and 77 shut until theapparatus is reset by pushing piston 90 back to its original position.

Normally, the forces on shaft 75 are balanced and the valve-pistons 76and 77 remain open. If, however, a leak occurs downstream of apparatus10 in either supply line 20 or return line 21, the forces on shaft 75move piston 90 to a position in which spring 92 takes over and shutsdown the hydraulic system downstream of the device.

Although mechanical embodiments have been discussed so far, electricalembodiments are also within the scope of this inventive concept. FIG. 3depicts electrical apparatus 100. Pistons 78 and 79 of apparatus 10 arereplaced with pressure transducers 101 and 102. In this description,substantially identical components of the previous embodiment, willretain the same reference characters. Pressure transducers 101 and 102are simple resistance-type diaphragm transducers that may be designed tomeasure pressures estimated on the order of 10 psi to 6000 psiaccurately. A simple relay 105 replaces pistons 80 or 90 in themechanical embodiment, and valve-pistons 76 and 77 are replaced byoff-the-shelf solenoid valves 106 and 107. The function of biasingspring 85 is replaced by the effect of resistors 108 and 109. Onebenefit of the electrical embodiment is that the pressure and returnlines do not have to be coincident.

Referring again to FIG. 3, the principle relied upon to generate thepressure differential is the same as the mechanical embodimentsdescribed above. The difference is that the pressure differential issensed electronically by the coaction of resistance-type diaphragmpressure transducers 101 and 102. Voltage _(o) is applied to one end ofthe transducers and a current flows through the resistors in thetransducers, through the balancing resistors 108 and 109, throughresistors R₃, and to ground. Resistors 108 and 109 function to providemass flow tolerance or compensation similar to the function ofpre-compressed spring 85 in the mechanical devices. Resistors 108 and109 balance out voltages V_(a) and V_(b) for a predetermined mass flowtolerance. A diode 110 is included to prevent any displacement of shaft75 when V_(b) is less than V_(a). This provides an equivalency to thecondition occurring in the embodiment of FIG. 1 when P_(r) is greaterthan P_(s) and piston 77 rests against wall 68. Relay 105 has inductorcoil 105a and switch 105b to provide essentially the same function aspiston mechanisms 80 and 90.

If the pressure differential differences between P_(s) and P_(r) arezero, or normal, then the voltages at relay 105 are equal or V_(b) isless than V_(a). No current flows through the relay's inductor and thecircuit to solenoid valves 106 and 107 remain open. Once, however, P_(s)is greater than P_(r) plus tolerance or compensation preset by themagnitudes of resistors 108 and 109, then V_(a) is less than V_(b). Thiscondition sets up a current through inductor coil 105a of relay 105. Thecurrent flow generates a magnetic field that attracts switch 105b inrelay 105 and closes the circuit to solenoid valves 106 and 107.Immediately, valves 106 and 107 close the downstream leak.

The specific mechanical and electrical embodiments described hereinaboveare intended to be illustrative of this inventive concept and are not tobe construed as limiting. It is to be understood that manyconfigurations, arrangement of constituents and modifications of theconstituents could be made by one skilled in the art without departingfrom the scope of this invention. It is well within the purview of oneskilled in the art to select suitable noncorrosive or corrosionresistant materials having sufficient strength.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically claimed.

We claim:
 1. An apparatus for shutting off a hydraulic circuitcomprising:a first sensor coupled to a hydraulic fluid supply line toproduce force F_(s) representative of flow of hydraulic fluid; a secondsensor coupled to a hydraulic fluid return line to produce force F_(r)representative of flow of hydraulic fluid; a compensator to create forceF_(c) representative of the rate of accumulation of hydraulic fluid insaid hydraulic circuit; and a shutoff mechanism connected to said firstand second sensors and said compensator.
 2. An apparatus according toclaim 1 in which said forces F_(s) and F_(r) are representative ofpressure differential forces P_(s) and P_(r), and consequently, the massflow difference between supply and return, respectively.
 3. An apparatusaccording to claim 2 in which said shutoff mechanism immediately shutsoff said supply line when F_(s) is greater than the sum of F_(r) andF_(c).
 4. An apparatus according to claim 3 in which said shutoffmechanism immediately shuts off said return line when F_(S) is greaterthan the sum of F_(r) and F_(c).
 5. An apparatus according to claim 4 inwhich said first and second sensors include Bernouilli devices providingpressure differential forces P_(s) and P_(r).
 6. An apparatus accordingto claim 5 in which said compensator includes a pre-compressed spring.7. An apparatus according to claim 6 in which said shutoff mechanismcomprises:a housing having a plurality of cylindrical compartmentsseparated by walls each having a bore aligned with each another; a shaftextending through all of the bores to permit reciprocal motiontherethrough; and at least one piston affixed to said shaft in each saidcompartment.
 8. An apparatus according to claim 7 in which saidpre-compressed spring is in one of said compartments to displace saidshaft in one direction.
 9. An apparatus according to claim 8 in whichfirst and second ones of said compartments respectively contain aportion of said supply line and said return line, and first and secondpistons are in said first and second compartments, respectively.
 10. Anapparatus according to claim 9 in which said first and second pistonsfunction as valves to close said supply and return lines when F_(s) isgreater than the sum of F_(r) and F_(c).
 11. An apparatus according toclaim 10 in which said F_(r) pushes against a third piston in a thirdone of said compartments to displace it in said one direction, and F_(s)pushes against a fourth piston in a fourth one of said compartments todisplace it in the opposite direction.
 12. An apparatus according toclaim 11 in which a fifth one of said compartments contains acircumferentially grooved piston, a sleeve having openings on saidrecessed piston, a spring pre-compressed between said sleeve and saidhousing, and a series of ball bearings carried in recesses in saidhousing to extend through said openings.
 13. An apparatus according toclaim 10 in which a fifth one of said compartments has conduitsconnected to said supply and return lines and contains a fifth piston.14. An apparatus according to claim 12 in which said fifth piston closessaid conduit to said supply line when F_(s) is not greater than the sumof F_(r) and F_(c) and opens said conduit to said supply line when F_(s)is greater than the sum of F_(r) and F_(c).
 15. An apparatus accordingto claim 1 in which said first and second sensors each include aBernouilli device and a pressure transducer to produce supply signalV_(a) representative of said force F_(s) and return signal V_(b)representative of said force F_(r), respectively, said compensatorincludes an impedance element coupled to each said pressure transducerto produce a voltage drop representative of rate of accumulation ofhydraulic fluid in said hydraulic circuit, and said shutoff mechanismincludes a relay coupled to a solenoid valve in said supply line and insaid return line.
 16. An apparatus according to claim 15 in which saidrelay is actuated to shut said solenoid valves and close said supply andreturn lines when V_(a) varies from V_(b) by a set amount.
 17. Anapparatus according to claim 16 in which mass flow is converted tovoltages V_(a) and V_(b).
 18. A leak detector and shutoff apparatuscomprising:means connected to a hydraulic fluid supply line for sensingpressure differential force P_(s) representative of flow of hydraulicfluid; means connected to a hydraulic fluid return line for sensing apressure differential P_(r) representative of flow of hydraulic fluid;means for compensating for rate of accumulation of hydraulic fluid in aninterconnected hydraulic element to create a representative pressureforce F_(c) ; and means connected to said P_(s) and P_(r) sensing meansfor shutting off said supply and return lines.
 19. A method for shuttingoff a hydraulic circuit comprising:sensing a pressure differential P_(s)representative of flow rate of hydraulic fluid in a supply line tocreate force F_(s) ; sensing a pressure differential P_(r)representative of flow rate of hydraulic fluid in a return line tocreate force F_(r) ; compensating for rate of accumulation of hydraulicfluid in an interconnected hydraulic element with a force F_(c) ; andshutting off said supply and return lines when F_(s) is greater than thesum of F_(r) and F_(c).